a. Field of the Invention
This invention relates to catalysts suitable for use in preparing fiber-forming polyesters and the method for making the same.
B. Prior Art
It is known to use germanium dixoide as a catalyst in a polycondensation reaction to produce polyesters. The germanium dioxide is sometimes added to the reaction mixture with a glycol, such as ethylene glycol. Unfortunately, the crystalline germanium dioxide has a very low solubility in the glycol, resulting in undissolved catalyst which remains in the polymer. The dissolved catalyst particles may result in undesirable physical characteristics in fibers made from the polymer. Also, low catalyst concentrations cause longer reaction times. Various approaches have been used to overcome the low solubility of the germanium dioxide in the glycol.
In addition to the difficulties encountered in dissolving germanium dixiode in a glycol, the use of this catalyst tends to result in poor color in fibers formed from a polymer made by using this catalyst. Also, germanium dioxide, when used as a catalyst in the formation of polyesters, tends to promote side reactions which form unwanted side products such as diethylene glycol. Other catalysts used in the production of polyesters require longer polymerization times and/or cause the polymer to have an unacceptable color.